Currently, most UV water treatment systems use low pressure cold cathode fluorescent (CCFL) mercury vapor lamps with a primary radiative emission of 254 nanometers (2,537 angstroms). This wavelength, which falls within the short wave UV-C band, is highly germicidal.
The CCFL UV lamps can be very effective in batch UV water purification systems, such as the system described in U.S. Pat. Nos. 5,900,212 and 6,110,424. However, the CCLF lamps are not well suited for wearable hydration systems. The lamps and their thermally insulating sleeves must be made from high quality, optical grade quartz, and thus, the CCFL UV lamp assemblies tend to be both costly and fragile. In addition, the CCFL UV lamps require high voltage AC power, and the circuitry needed to deliver this power is complex and relatively expensive, particularly if the input is from a DC source such as a battery.
The lamps also require a significant “warm-up” period during which lamp output “ramps up” from zero to full power. During this “ramp-up” period, any water flowing past a CCFL UV lamp will not have predictable or uniform UV exposure. As a result, the efficacy of the treatment of water in such a flow-through system, from a micro-biological standpoint, becomes unpredictable and unreliable. For this reason, safety dictates that CCFL UV lamps be allowed to “ramp-up” to a steady-state output before water flow past the lamp is permitted. Achieving this steady-state output may take up to several minutes.
In a wearable flow-through hydration system or other intermittently operated on-demand flow-through systems, water consumption is not only intermittent but sudden and unpredictable. Accordingly, the CCFL UV lamps must, for safe operation, have been “ramped-up” to a steady state output before the water is allowed to flow past. The user must thus either keep the CCFL UV lamp on all the time or turn on the lamp for up to several minutes prior to each use, in order to allow for the “ramp-up” to steady state output. Neither of these scenarios is particularly desirable. In the first, the lamp must be kept on all the time and consumption of limited battery power quickly becomes a problem. In the second, the lamp must be turned on minutes before taking each drink and there is an obvious inconvenience.